Automatic grinding apparatus and grinding method



March 8, 1966 J. D. ABBOTT ET AL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24. 1961 14 Sheets-Sheet 1 James D AbbozL Char/e5 H Chano/Aer Franc/'5 E F/aherg n WK .w wmmf Wmw-m ymaw @www AH March 8, 1966 J. D. ABBoT'r ET AL AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD 14 Sheets-Sheet 2 Original Filed Nov. 24, 1961 MNN [f1 z/en o rs fmes D. Abbott' Char/e5 l. C ha )1d/er Franc/'5 E. F'la hery Angus WMM/(femm March s, 196s J, BABBO-r1 E-rAL I 3,238,615

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 5 In l/e n fors Tanzes D. Abbott Char/es )t (hand/er FdnCiS E. FIahery Angus VV-Mac/Ierngn Harry Lambo By their Affrneys agi/14% x March 8, 1966 .1. D. ABBOTT ETAL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 4 Grinding Headl l Grinding Head f3 M4 l 1013 Grinding Head #Z Grinding Head t1 706 I n Ven tor .7d/nes D. Abbo (hdr/e5 H. (hand/er Fran Us E. F'Iq hery Angus W Mac/f lerne/1 March 8, 1966 J. D. ABBOTT ETAL AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 5 In Ven 'to rs J'ames D. Abbott Char/es H. C /1 a 11d/er F'anc/'S E. Flahery Angus W Mac/Hernan Harry Lambry B] their .4t ornejvs March 8, 1966 J. D. ABBOTT EIAL 3,238,675

AUTOMATIC GRINDING APPARATUS AND @BINDING METHOD original Filed Nov. 24, 1961 14 sheets-sheet e fili/Avy( 212 In Ve n to f5 fam@ D. Abbott Char/e5 H Chnc//er Franc/'S E, Flaherty Angus W MMX/ema Haw .Lambo By their At cmq/5 March 8, 1966 J. D. ABBOTT ET AL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 7 w m lign n mmf@ m Obahunw WIN md eDEWah VS C m u) nmrngw Idhamna TCVAH March 8, 1966 .1. D. ABBOTT ETAL AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 8 W Mac/(mr L ambo] Inl/ent Iam e5 D A bb o# Char/e5 H. (hand/e Francis E. F'aher Angus Harr efr Aitor 17M QN /k NMNT www f March 8, 1966 J, D. ABBQTT ETAL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD 14 Sheets-Sheet 9 Original Filed Nov. 24, 1961 k rn e r a M wm r o nw? J 0b dlmbm mwmfmm WQHEMMW NSSW A e@ c lm SAQ T. m r n w r e a www IMFAHOWM w53 March 8, 1966 J, D, ABBQTT ET AL AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD 14 Sheets-Sheet l1 Original Filed Nov. 24. 1961 Smm mvg N 2.36@

In uen tors. Jmes D. Abbo Char/@.5 H. (hand/el' Franc/5 E. F'lqherb' Angus W/Wacf//fmn Har/J( Lambo/v March 8, 1966 J. D. ABBOTT ETAL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet l2 Fly 19 w I2 3456789 |.1|||||||x||||||f| ,uml Inventors *Mmmfmes D' Abbott I Char/esl( Ccmd/er im mlm/5 E. naher@ l 64I 1 Angus WMac/f/'eman Harry I lmbqy B] the/r Attorneyg March 8, 1966 J, D, ABBOTT ET AL 3,238,675

AUToMATIC GRINDING APPARATUS AND GRINDING METHOD 14 Sheets-Sheet 15 Original Filed Nov. 24, 1961 I nl/en fors:

Iam es D. Abbo H' Char/e5 H. C60/1 d/er Fran C15 E. F'lherry Angus M/Machlernan Harry Lam Iggy By #heir/1 zarneys WM @am l March 8, 1966 1. D. ABBOTT ETAL 3,238,675

AUTOMATIC GRINDING APPARATUS AND GRINDING METHOD Original Filed Nov. 24, 1961 14 Sheets-Sheet 14 United States Patent O1 31 Claims. (Cl. 51-165) This is a continuation of application Serial No. 154,518 filed on November 24, 1961, now abandoned.

The present invention relates generally to control systems and methods and more particularly to a control system and a method for adjusting grinding devices or the like in response to information derived from the surfaces worked upon.

Although the invention is applicable generally to grinding machines and polishing machines in which elongated stock is surface ground or polished as it is moved past rotating abrading devices, it will be described herein for use in connection with the sharpening of razor blade strip.

In making razor blades it is convenient to sharpen a razor blade strip and then cut the sharpened strip into individual blades. The sharpening operation may include one or more grinding operations, a honing operation, and a stropping operation performed sequentially on the blade strip as it is moved along at a predetermined speed. In order to obtain razor blades of uniform shaving quality it is necessary to maintain the included angle of the cutting edges, the widths of the various facets of the bevels, the width of the blades and the location of the central slot within certain predetermined limits. The most critical part of the sharpening operation, insofar as the geometry of the sharpened blade edge is concerned, is the lirst grinding operation. If this grinding operation is performed accurately, the subsequent sharpening operations can be performed with only infrequent minor corrections. The invention disclosed herein will be described with specific reference to the grinding operation, although it is applicable to all of the sharpening operations involved. The desired half-angle ofthe ground edge is normally determined by the design of the grinding apparatus and remains substantially constant as long as no `structural changes are made therein. Corrective changes in the bevels of the edge and of the width of the sharpened strip can be made by moving the grinding heads in or out on their beds as required, thereby increasing or decreasing the amount of material removed. However, since the blade width is a function of the material removed, adjustments of the grinding heads to change either the relative sizes of the bevels or the width of the strip must be correlated.

Skilled grinders can by examination of the iinished ground edges of periodically sampled blades detect small deviations from a preset standard and will know from past experience which grinding head or heads should be adjusted, and by how much, in order to bring the blade edge geometry and the width of the blade into correspondence with the standard. As a practical matter, considerable imbalance between the two opposite ground bevels of the edge can be tolerated without effecting the quality of the finished product but by frequently adjusting the grinding heads to balance the bevels (i.e. to make them equal) any drift towards a condition that could affect the quality of the end product can be headed olf.

Accordingly, a general object of the present invention is to provide a system and a method for automatically controlling edge forming devices operating on moving elongated stock so as to correct for deviations in the 3,238,675 Patented Mar. 8, 1966 ice geometry of the formed edge from a desired edge geometry.

Another object of the invention is to provide a system and a method for automatically controlling edge forming devices operating on a moving strip so as to correct for deviations from a predetermined desired width and/or half-width of the sharpened strip.

Still another object of the invention is to provide a control system and a method for automatically positioning edge-forming devices operating on a moving strip so as to adjust them simultaneously and in a coordinated manner to provide a predetermined bevel relationship as well as a desired blade width and/ or half-width.

A further object of the invention is to provide a control system for scanning the two Aopposite bevels of a ground edge, comparing the widths of these bevels, producing an error signal as function of the dierence in width of these bevels, and automatically adjusting the grinding heads with respect to the blade strip in response to this signal so as to reduce or eliminate the bevel imbalance from which it was derived.

A further object of the invention is to provide a control system for automatically positioning grinding heads operating on a moving metal strip for double-edged blades so as to adjust the grinding heads for a predetermined bevel relationship and a predetermined blade half-width.

A further object of the invention is to provide a control system for detecting certain parameters of a ground strip for double-edged blades, developing error signals as a function of deviations from predetemined parameters and adjusting the grinding devices so as to reduce or eliminate deviations from such predetermined parameters.

A still further object of the present invention is to provide novel means for detecting the width of a bevel of an edge of a ground razor blade strip.

A still further object of the invention is to provide an optical system for periodically scanning a portion of a ground bevel and producing a signal having a time duration as a function of the width of such bevel portion.

Additional objects of the invention will be apparent from the following description of an illustrative embodiment thereof.

The invention accordingly comprises the apparatus having the construction, combination of elements and arrangement of parts, and the method comprising the several steps and the relation of one or more of such steps with respect to others, which are exemplified in the apparatus and method hereinafter described and illustrated in the accompanying drawings wherein like reference numbers designate like parts, and in which:

FlG. 1 is a block diagram of the entire system;

FIG. 2 is a view in side elevation of the bevel scanner unit with portions of the housing broken away;

FIG. 3 is a plan view of the bevel scanner with the cover removed;

FIG. 4 is an end view lof the microscope tube taken on line 4-4 of FIG. 3;

FIG. 5 is a cross-section view of the microscope adjusting mechanism taken on line 5-5 of FIG. 2;

FIG. 6 is a schematic representation of ythe optical system of the scanner;

FIG. 7 is a view in side elevation of the half-width detector assembly;

FIG. 8 is a view in front elevation of the half-width detector;

FIG. 9 is an enlarged view in side elevation of the blade strip supporting unit;

FIG. l0 is an enlarged fragmentary isometric view, partly in section, of the blade strip supporting unit;

FIG. ll is a diagram of the photo detector and ampliier circuit;

FIG. 12 is a circuit diagram of the pulse width detector and amplifier unit;

FIG. 12A shows waveforms that illustrate the operation of the pulse width detector of FIG. 12;

FIG. 13 is a circuit diagram of the phase sensitive detector and amplifier unit;

FIG. 14 is a circuit diagram of the programmer;

FIG. 15 is an isometric, partly exploded view illustrating the general construction of a meter relay;

FIG. 16 is a timing diagram of cam operated contacts that control the operation of the programmer;

FIG. 17 is a grinding head correction chart;

FIG. 18 is a schematic diagram of a pulse train generating unit;

FIG. 19 illustrates the phase relationship between two pulse trains applied to respective field windings of a motor that positions a grinding head;

FIG. 20 is a view in side elevation, partly in section, of a grinding head assembly;

FIG. 21 is a plan view of a grinding head assembly;

FIG. 22 is a view in front elevation of the grinding head assembly; and

FIG. 23 is a plan view of a grinding machine illustrating the positions of the bevel scanners and the half-width detectors with respect to the grinding heads.

GENERAL DESCRIPTION The grinding system is accordance with the invention is shown in block form in FIG. 1. Generally speaking, the system operates on the zero-seeking principle. It senses the bevels and the width of a moving sharpened razor blade strip and determines deviations from bevel balance or some other desired bevel relationship and deviations of the blade half-width from a predetermined standard; it decides from this determination what correctional movements are needed by the grinding heads of the machine in order to reduce the deviations to zero; and it then actuates the grinding heads to accomplish those movements.

For the purpose of illustrating the nature of the invention, a specific embodiment of the invention will be described as it pertains to the grinding of the four bevels of a moving razor blade strip for double-edged razor blades; but it will be obvious to those skilled in the art that the invention has wide applications in the field of material removal and is not limited to the specific utilization illustrated. Thus, the invention is applicable to the formation of sharpened edges such as by grinding, honing, stropping or by other means and is particularly applicable to the formation of edges on razor blade strips.

In the following description of the invention, it will be assumed that a razor blade strip 10, FIG. 1, is moving toward an observer. The two top bevels will be referred to as bevels 1 and 3 and the two bottom bevels as bevels 2 and 4. The distance measured from the upper edge of the center slot to the apex formed by the bevels 1 and 3 of the blade strip will be referred to as the top halfwidth, and the distance from the lower edge of the center slot to the apex formed by the bevels 2 and 4 will be referred to as the bottom half-width. The grinding head that grinds bevel 1 will be referred to as grinding head 1 and the grinding head that grinds bevel 2 as grinding head 2 and so on.

Referring now to FIG. l for a general description of the system illustrated therein, optical scanners 11 and 12 are associated with the top bevels 1 and 3, respectively, of: the blade strip and generate electrical signals as a function of the widths of the respective bevels scanned. The signals derived from the scanners 11 and 12 are, respectively, amplified in amplifiers 13 and 14, modified and amplified in pulse width detectors and amplifiers 1S and 16, clipped an integrated in clippers and integrators 17 and 18, and the integrated signals are amplied by D.C. amplifiers 19 and 20. The D.C. potentials from the amplifiers 19 and 20 are compared by a meter relay 21 and by a visual meter 22. A blade half-width measuring device 23 develops A.C. error signals as a function of the sense and magnitude of deviations of the top halfwidth of the blade strip 1G from a predetermined standard 24, which signals are amplified by an amplifier 26 and converted into a corresponding D.C. error signal by a phase sensitive detector 27, and the resulting D.C. error signal is amplified by an amplifier 28 and applied to a meter relay 30 and a visual meter 31. A system which may be an exact duplicate of that operating on the top half of the blade strip operates on the bottom half thereof with the exception of the meter relays 21 and 30 which are used alternately for both systems. The outputs from the meter relays 21 and 30 are applied to a programmer 32, the output of which is connected to grinding head controls 34, 35, 36 and 37 which actuate grinding head displacing devices in accordance with a correction sequence determined by the programmer.

The optical scanner 11 associated with bevel 1 scans this bevel successively from a predetermined point along the bevel as determined by a fixed mask to and beyond the heel (where the ground edge starts), and produces raw electrical signal pulses each of which has a detectable portion proportional to the width of the portion of the ground bevel scanned. These raw signal pulses are operated upon in the pulse width detector and amplifier 16 which produces amplified square wave pulses corresponding in width to the detectable portions of the raw pulses. These square wave pulses are clipped to an exact predetermined amplitude and then integrated to produce a DC. potential which is the average of the width-potential product of a series of such pulses. This D.C. potential is amplified by a D.C. amplifier 16 and applied through a double-pole, double-throw, cam-operated switch 40 to one side of the meter relay 21. The bevel 3 of the blade strip is similarly scanned by the optical scanner 12 and the signals derived from this scanner are operated upon as described above in connection with signals derived from the scanned 11 to produce a D.C. po .tential at the output of the D.C, amplifier 20 proportional to the distance between the heel of the ground bevel 3 and the cut-off point provided by the scanning mask, which D.C. potential is applied to the other side of the meter relay 21.. The cut-off points of the scanning masks of the two scanners 11 and 12 are so adjusted that when a blade strip is scanned in which bevels 1 and 3 are in exact balance, pulses of exactly the same width are produced at the outputs of the pulse width detectors and ampliers 15 and 16. Similarly, the DC. amplifiers 19 and 20 are so adjusted that the output potentials therefrom are exactly equal when the bevels 1 and 3 are in exact balance. It will be assumed herein that the visual indicating meter 22 and the meter relay 21 will be deiiected in a positive sense when the bevel 3 is larger than the bevel 1 and in a negative sense when the bevel 1 is larger than the bevel 3.

A deflection of the meter relay 21 in either positive or negative sense indicates that a corrective positioning is required of the grinding heads operating upon the bevels 1 and 3 so as to bring the bevels into balance. However, any change in the position of one or the other of the grinding heads 1 and 3 will result in a change in the ha1fwidth of the blade, so that the size of the half-width of the blade must also be taken into account in the determination of the grinding head movements required in order to correct for the bevel imbalance indicated. To this end the half-width detector 23 is provided, which generally comprises a differential transformer actuated by a sensing element engaging the top edge of the blade strip 10 operatin(r in conjunction with a reference device 24, which may be a similar differential transformer, to produce output signals of a polarity indicating whether the blade half-width is too large or too small with respect to a predetermined target and of an amplitude indicating the amount of deviation therefrom. The signals from the half-width detector 23 and the reference device 24 are amplified by the amplifier 26 and detected by the phase sensitive detector 27, and the resulting signals from the detector are applied to a differential D.C. amplifier 28 which produces a difference in D C. potentials on two output leads of a polarity and potential reflecting the sense and magnitude of the deviation of the measured half-width from the target. The visual indicating meter 31 and the meter relay 30 will be deflected in a positive sense when the top half-width of the blade is too large and a negative deflection when the top half-width is tooV small.

The programmer 32 selects appropriate correction sequences from a predetermined program in accordance with the deflections of the meter relays 21 and 30 and transmits the appropriate directions to the grinding head controls 34 and 3S that will effect the positioning the grinding heads 1 and 3 to correct any imbalance between the ground bevels 1 and 3 and at the same time correct for any blade half-width deviation. After having cornpleted the sampling of the error signals derived from the top half of the blade strip, the programmer operates the switches 40 and 42 to disconnect the D.C. amplifiers 19 and 20 from the meter relay 21 and connect thereto the corresponding D.C. amplifiers 44 and 46 associated with the bevels 2 and 4, respectively, and disconnect the D.C. amplifier 2S from the meter relay 30 and connect thereto the corresponding D.C. amplifier 48 associated with the bottom half-width detector 50. The meter relay 21 will now respond to the bevel balance error signals derived from the bevels 2 and 4 and the meter relay 30 will respond to the bottom-half-width error signals. The programmer 32 now selects the appropriate correction sequences for the grinding heads 2 and 4 and sends the appropriate directions to effect the necessary corrections to the grinding head controls 36 and 37, after which the programmer will again operate the switches 40 and 42 to transmit directions to controls 34 and 35 and so on. The programmer 32 will thus alternately sample signals derived from the top half of the blade and from the bottom half of the blade and effect the grinding head corrections required. The timing of the system is such that the portion of the blade strip that is ground by the grinding heads after the grinding head corrections have been made reach the bevel balance scanners and the halfwidth detector before the next sample is taken. The entire system is adjusted so that the correction set into the grinding heads will not over-correct for the errors detected in the blade strip geometry but will always tend to reduce such errors to zero. Means is provided, which will be described hereinafter, which will reduce the amounts the grinding heads are moved in response to directions from the programmer 32 so as to prevent any overcorrection, and, hence, prevent any tendency of the system to hunt or oscillate.

BEVEL SCANNERS The four optical scanners associated with the respective bevels of the ground razor blade strip may be identical in their operating principles and are mounted so that the axis of each scanner is substantially normal to the plane of the ground bevel with which it is associated. The optical scanner 11 associated with bevel 1 is shown in FIGS. 2 and 3 together with a portion of the diametrically opposite scanner 12 associated with bevel 3.

Each scanner includes a source of light 100, which directs a concentrated beam of light onto the freshly ground bevel with which it is associated, a microscope 192 disposed so as to cover the portion of the ground blade bevel that includes the heel (where the ground edge starts), a scanning mechanism 104 and a phototube detecting and amplifier unit 106.

The microscope 102 includes an objective 110, FIG. 3, threaded into the end of a metal tube 112, and an eyepiece 114 threaded into the opposite end of the tube.

The microscope tube 112 is received within a rigid outer tube 116 and is adjustably secured thereto by means of a clamp ring 118 which embraces a split end 120 of the tube 116. The clamping tube 116 is pivotally mounted in a yoke 122 of a microscope supporting bracket 124 by means of a collar 126 supported in the yoke by pivot pins or trunnions 128.

In order to permit the microscope to be adjusted in elevation, there is provided an adjusting mechanism that includes a yoke 136 supported on an eccentric shaft 132, FIG. 5. The tube 116 is held in the yoke 130 by means of a collar 134 pivotally mounted in the yoke by pivot pins 135. A downwardly extending neck 136 of the yoke is received between a pair of ears 138 and 139 on the bracket 124 in which the eccentric shaft 132 is journaled. The eccentric shaft 132 includes an expanded hub 140 received within the ear 138 and a reduced hub 142 that extends through and beyond the ear 139 and has a spur gear 144 rigidly secured thereto by means of a nut 146 screwed onto the outer threaded end thereof. It will be appreciated that as the eccentric shaft 132 is rotated by rotation of the gear 144 in one direction or the other the yoke 13@ and hence the end of the tube 116, attached thereto will be moved upwardly or downwardly. A worm gear 148 (FIG. 2) is rotatably mounted in journals 150, which may be formed integrally with the microscope bracket 124, and the operating shaft 151 therefor extends upwardly and terminates in a finger knob 152 by which the worm gear 148 can be manually rotated in one direction or the other.

A ratchet wheel 154 secured to the shaft 151 and a ratchet spring 156 mounted on the bracket 124 are provided for maintaining the worm gear in its set position. The bracket 157 for supporting the light 100 may conveniently be mounted on the side of the bracket 124 by means of a mounting screw 158.

The tube 116 extends through an opening 160 in the microscope housing 162 and supports the housing 164 of the scanning mechanism 104 and the housing 165 of the phototube detecting unit 106. The housing 164 is securely and rigidly clamped to the tube 116 by means of a pair of set screws 166. The opening is suiiiciently large to accommodate the necessary adjustments of the microscope. The tube 116 is provided with a transverse slot (FIG. 3) near the outer end thereof for receiving the peripheral portion of a rotating scanning disc 172. A mask 174 having an aperture 175 of a shape shown in FIG. 6 is fitted within the end of the tube 116 to limit the light reflected from the bevel being scanned to a predetermined portion of the bevel. The mask 174 is cemented to an end piece 176 secured into the end of the tube 116 by a set-screw. The scanning disc 172 is rigidly mounted on the drive shaft 177 of an induction motor 178 and is provided with a plurality of equally spaced radial slots 186 (FlG. 6). The phototube detecting unit 1136 mounted within the housing 165 includes a phototube 181 which may suitably be a photomultiplier tube such as type 931A, manufactured and sold by R.C.A., Camden, New Jersey.

The aperture of the mask 174 (FIG. 6), transmits the image of the sharpened bevel 1 magnified by the objective 11) and eyepiece 114, starting at la certain point between the heel 182 of the bevel and the ultimate edge and extending to a point well below the heel. The fiank of the razor blade strip reflects far less light into the scanner than the freshly ground bevel surface and as a slot in the scanner disc 172 sweeps across the opening 175 in the mask, a sharp increasein the light intensity is transmitted through the slot as soon as it encounters the image and a drop in light intensity occurs when the slot passes the line of demarcation (referred to above as the heel) in the imag-e between the ground surface of the blade strip and the fiat fiank thereof. This sharp decrease in the light intensity is used in accordance with the present invention to indicate the time at which the split passes the heel of the ground surface. The aperture 175 in the mask 174 is formed with a taper at the bottom to prevent the transmitted light from being shut off with sufficient abruptness to cause a spurious response in the detecting circuit. If equal bevels yare desired, the scanning units associated with the bevels 1 and 3 are adjusted while scanning a test blade having balanced bevels. The two scanning units are adjusted by turning the finger knobs 152 to either raise or lower the microscopes as required until the light reliected from the bevels is tr-ansmitted through the opening 175 of the mask 174 of each unit for exactly the same period of time. The two microscopes are thus set to a certain predetermined standard bevel balance to which it is desired to bring the bevels of a sharpened razor blade strip being sampled by the two scanning devices. A sharpened razor blade strip moved past the oppositely mounted scanning units will, if the ground bevels balance exactly, cause the reliected light from the ground bevels to be transmitted through the slots 189 of the scanning discs 172 for exactly the same proportion of the total cycle. Since the duty cycle, i.e. the mark-to-space ratio of the pulse pattern, is a quantity which is established uniquely by the distance between the top of the opening 175 in the mask 174 and the image of the heel on the one hand and the spacing between the successive slots 189 of the disc 172 on the -other hand, the speed of the disc is not important. A change in the speed of the discs would only result in a narrowing or widening of the entire pulse pattern which would not affect the integrated value of the pulses. Since only the mark-to-space ratio of the pulses is measured, the only requirement for proper operation is that sufficient reected light is obtained to produce a signal across the output of the phototube that has a detectable rise in level as the slot 189 in the disc 172 enters the opening 175 of the mask 174 and a detectable drop when it passes from the ground edge of the razor blade onto the ilank thereof. By masking the edge of the razor blade, errors which might result by scanning the ragged raw edge of the freshly rough ground blade are avoided. lt will 'be appreciated that the two scanners in etfect determine whether the two heels of the two bevels being compared are at the exact same level, and since each of the grinding heads grinds the bevels at a predetermined equal angle with -respect to the central plane of the razor blade strip, the bevel widths will be exactly `alike as long as the heels thereof are perfectly aligned, Variations in intensity of the transmitted light caused for example by variations in the reflectivity of the ground edges, by dirt, grime and cutting oil thereon or by an oil film or particles adhering to the objective 11@ or by variations in photomultiplier or amplifier sensitivity will not adversely affect the effectiveness of the scanner as lon" as the transmitted light is above a certain minimum level.

The -microscope bracket 124 of the scanner 11 for bevel 1 '1nd the corresponding bracket of the scanner 12 for bevel 3, may 'be Asupported by a base 183, FIG. 2, which is suitably supported on the bed of the machine itself such as by spanning a pair of rails 134 running on each side of the machine lengthwise thereof and parallel to the movements of the r-azor blade strip. The common housing 162 for the two microscope units 102 is provided with a cover 163 that prevents entry of undesired light which, if modulated, might cause spurious signals, and further prevents outside dirt and fumes from entering the enclosure while permitting access to the finger knobs 152 for adjusting the microscopes whenever necessary Secured to the base 133 between the bevel scanners 1 and 3 is a blade strip supporting bracket 185, FIGS. 7 and 8, which Ialso serves to support the half-width detector 23. The bracket 185 is provided with a side recess 186 for receiving a blade strip supporting stlucture 187, and with a horizontal rail 188 within the recess for supporting the half-width detector 23. The half-width detector 23 includes a block 189 resting on the rail 188 and 9 bolted to the bracket and having a horizontal channel 19t) formed adjacent the lower edge thereof. The block 189 is recessed to receive a plate 191 having a channel 192 complementa-ry to the channel 190 in the block. The bottom edges of the block 189 and the plate 191 are spaced by a dist-ance suflicient to permit the blade strip 1t) to pass therebetween. The plate 191 may suitably be bolted to the block 189. A carbide key 194 is loosely confined within the enclosure defined by the channels 19t) and 192 and rides on the top edge of the razor blade strip 10. The top surface of the Icarbide key 194 is provided with a centrally located recess 196 which forms a shoulder 197 on each side of the block 1F9 that retain the key in position and prevent it from longitudinally following the moving razor blade strip 10 on which it is resting. A further recess 198 is provided in the bottom surface of the carbide key 194 at the location of the optical scanners so as to expose the blade strip bevels thereto. Extending downwardly from the top of the block 189 and centrally located therewithin is a bore 199 through which extends a pin 251i resting on the top surface of the carbide key 194. The top surface of the block 189 is provided with a well 261 centered with respect to the bore 199 and adapted to receive a differential transformer 202. A movable core 223 of the transformer 262 is threaded onto the .pin 200 and a second piu 204 is threaded into the top of the core 203 and terminates in a shouldered spring abutment 295 for receiving the end of a compression spring 2% contained within a U-shaped bracket 297. The other end of the spring 266 is received by an abutment 208 formed at the end of a spring adjusting plug 2119 threaded into the end of the bracket 267.

The blade strip supporting structure 187 includes a supporting block 210 received within the recess 186 of the bracket at the bottom end thereof and rigidly secured thereto by means of bolts 211. Integrally formed on the block 210 is an upwardly extending wedge 212 carries blade strip supporting plates 214 and 215 on the respective wedge surfaces thereof. The plates 214 and 215 are secured to the respective inclined wedge surfaces by means of bolts 216 extending through the wedge 212 and through elongated openings 218 in the plates 214 and 215 which permit limited vertical adjustments thereof. The upper ends of the plates 214 and 215 are spaced apart by a distance sufficient to permit a blade strip to move therebetween. The plate 214 is provided with a longitudinaly extending groove 217 (FIGS. 9 and l0) and seated within a channel 219 of the plate 215 is a key 220 that extends part way into the groove 217 of the plate 214. The key 22u is tapered at both ends. The spacing between the key 22) and the bottom of the groove 217 is sufficient to permit the joined sections of the razor blade strip between the central slots therein to bend around the key 220 as shown in FIG. 10. The portions of the razor blade strip adjacent the slots will not, however, bend around the key 220 but the lower edges of the upper portions will rest on the top flat surface thereof. ItV will thus be appreciated that as the razor blade strip is moved through the spacing between the plates 214 and 215 the lower edges of the razor blade strip immediately above the central slots will rest upon the top surface of the key 220 while the joined portions of the strip between the slots will bend around the key within the groove 217 of the plate 214. The carbide key 194 -biased downwardly by the spring 206 will press the razor blade strip firmly against the top surface of the key 220.

The razor blade strip holder 187 supports the moving blade strip 10 in such a position that the sharpened edge thereof will be disposed at all times between the -two channels and 192 in the block 189 and the plate 191, respectively, whereby the carbide key 194 will always engage and ride on top of the sharpened edge of the strip.`

9 PHOTOTUBE AMPLIFIER AND PULSE WIDTH DETECTOR AND AMPLIFIER A circuit for converting the variations in the intensity of the light beam passing through the slots 180 of the scanning disc 172 into corresponding electrical signals is illustrated in FIG. 11. The phototube 181 which may suitably be a 931-A type tube such as manufactured by R.C.A., Camden, New Jerse is connected as shown and as recommended by the manufacturer. The output signal from the phototube 181 appears across a resistor 222 connected between the tenth and last plate 224 and ground. The output signal across the resistor 222, which signal has a time duration equal to the time it takes the scanner to sweep across the exposed portion of the blade strip edge being sampled, is applied to the input of an amplifier tube 226 of the amplifier 14 through a coupling capacitor 227 and the output from the amplier tube 226 is connected to the grid of a second ampliiier tube 228 through a coupling capacitor 229 and a potentiometer 236. The amplitude of the output signal from the amplifier tube 228 appearing on the output terminal 232 and applied to the input of the pulse width detector and amplier 16 (FIG. 12) can be adjusted by adjusting the slider of the potentiometer 230.

The raw signal pulse 240 (FIG. 12) appearing on the terminal 232 and derived from the optical scanner and the phototube detecting and amplifier circuit (FIG l1) is a negative-going one having a time duration between the sharply falling edge 244 and the sharply rising edge 245 thereof proportional to the width of the portion of the bevel scanned, i.e. the portion between the point at which the reiiected light enters the opening 175 of the scanner mask 174 (FIG. 6) and the heel 182 (Where the ground surface starts). The amplitude of these pulses may vary due to inherent changes in reectivity of the freshly ground surface or the sensitivity of the scanner, but variations in the amplitude of successive signals from one scanner or of signals derived from diterent scanners are not a problem so long as the pulses are of su'icient amplitude to permit the time duration thereof to be detected.

The differential amplifier 16 is adapted to produce essentially square-sided amplified pulses having a time duration equal to the time duration between the sharply falling and rising edges 244 and 245 of the raw input pulse 240, thereby cutting off the trailing portion 246. The differential amplifier includes a pair of tubes 250 and 251, which may be the two halves of a double triode, having the cathodes thereof connected to ground through a common cathode resistor 252. The plate of the tube 250 is connected to a D C. line 254 through a load resistor 256 while the plate of the tube 251 is connected directly to lthe D.C. line. The input pulses 240 are applied to the grid of the tube 250 through a `coupling capacitor 257 and a resistor 258. The grid of the tube 250 is connected to the grid of the tube 251 through a resistor 259 shunted by a diode or rectifier 260. The juncture between the coupling capacitor 257 and the resistor 258 is connected through a resistor 261 to a positive potential conveniently provided at the juncture 262 between resistors 263 and 264 connected in series across the D.C. line 254 and ground. The grid of the tube 251 is connected to the positive juncture 262 through a storage capacitor 265.

For a better understanding of the operation of the detector and ampliiier circuit 16, reference is made to FIG. 12A wherein the signal wave-form 240 :appearing at the juncture 266 and the waveforms 267 and 269 appearing at the grids of the respective tubes 250 and 251 are shown superimposed above the resulting waveform 271 that will appear at the plate of the tube 250. The potential at the grid 250 will be positive with respect to the potential at the grid 251 just before a signal pulse is applied to the terminal 232 after the circuit has 10 been in operation for a sufficient length of time to become stabilized.

The descending steep portion 244 of the signal waveform 240 (representing an input pulse) will drive the grid of the tube 250 to the same potential as the grid of the tube 251 and this sudden differential change in potential of the two grids will result in a sharp rise in plate potential as shown in the wave-form 271 representing the output pulse. The plate potential of the tube 25() will thereafter remain at a substantially constant value as long as the potentials at the two grids are equal to each other, which is a characteristic of differential amplifiers well known to those skilled in the art.

The potentials at the grids of the tubes 250 and 251 will not follow the descending portion 244 of the waveform 240 because of the capacitor 265 which discharges through the diode 260 and the resistors 258 and 261 but will go negative more slowly at a rate determined by the values of the resistor 258 and the capacitor 265 in accordance with the well-known law applying to resistance-capacitance circuits. Since the impedance of the diode 260 to current ow (conventional) from the capacitor 265 to the resistor 258 is negligible, the potentials at the grids of the tubes 250 and 251 will be substantially equal during this descent and hence no change will occur in the plate potential of the tube 250. Transients indicated at the bottom of the wave 240 will have no effect on the output signal as long as they do not rise above the potentials at the grids of the tubes 250 and 251.

The ascending portion 245 of the waveform 240 will cause a current ilow to the capacitor 265 ythrough the resistors 258 and 259 when it rises above the potentials at the grids of the tubes 256 and 251 and a difference in potential equal to the voltage drop across the resistor 259 will be developed thereacross resulting in a sudden conduction of the tube 250 to drop the potential on the plate thereof, as indicated in the output pulse 271.

It will be appreciated that the width of the squared portion of the output pulse 271 will correspond to the width of the input pulse 240 between the steeply descending portion 244 and the steeply ascending portion 245 as long as the values of the capacitor 265 and the resistor 258 are selected so that the slowly descending portions of the waveforms 267 and 269 intercept the steeply ascending portion 245. If these descending portions descend too rapidly they might be intercepted by transients at the bottorn of the waveform 240 to cause the tube 250 to conduct prematurely and if too slow they might be intercepted by the trailing portion 246 instead of the ascending portion 245 to make the output pulse too long.

The output pulse 271 at the plate of tube 250 is applied to a network consisting of a capacitor 272 and a resistor 273 in series, the values of the capacitor and the resistor being so chosen that the waveform 271 appears substantially unchanged at the juncture of the capacitor 272 and the resistor 273. This juncture is connected to one grid of tube 268, the cathodes of which are returned directly to ground. This connection effectively limits the positive excursions of waveform 271 appearing at the grid of tube 268 to ground potential. It will be appreciated that the potential at the grid of tube 26S will therefore be suf-` tticiently negative to cut off the plate current of tube 268 except during the interval between the steeply ascending portion of waveform 271 and the steeply descending portion thereof, and that during the said interval the plate current will remain substantially constant. This results in the amplified and inverted replica 270 of the topmost portion only of waveform 271 appearing at the plate of tube 268.

The amplified negative output pulse 270 from the tube 268 is applied to a pulse clipping network that includes a coupling capacitor 281 and a resistor 274 connected in series to a terminal 275 which is connected to ground through a rectifier 276, and through a rectifier 280 and a resistor 282 connected in parallel to a positive potential conveniently provided at the juncture 277 between resistors 278 and 279 connected in series across the D.C. line 254 and ground. The terminal 275 is connected to the grid of a D.C. amplifier tube 284 of the amplifier 20 through a resistor 286 which forms an integrating circuit with a capacitor 287 connected between the grid of the tube 284 and ground. The rectifier 276 is poled so as to conduct when the potential at the terminal 275 tends to go below ground potential and the rectifier 280 is poled so as to conduct when the potential at this terminal tends to go more positive than the juncture 277.

The approximately square wave 270 from the amplifier 16 is of sufiicient amplitude to tend to drive the terminal 275 above the positive potential of the juncture 277 and below ground potential, but since the rectifiers 276 and 280 are poled so as to limit the excursions of this terminal to these potentials, a square wave 288 of an exact, predetermined amplitude will always appear on this terminal.

The raw signal pulse similar to the pulse 24) derived from the scanner 12 which operates on the opposite bevel 3 of the blade strip 10 is applied to the input of the differential amplifier 15 which preferably is identical with the differential amplifier 16 described above. The output pulse from the amplifier y15 is connected to a terminal 289 through a capacitor 293 and a resistor 291 and the terminal 239 is connected to ground and to the positive juncture 277 through rectifiers 292 and 293 respectively. The terminal 289 is connected to the grid of a D C. amplifier tube 294 of the amplifier 19 through a resistor 295 and a capacitor 297 is connected between the grid of the tube 294 and ground. The clipper and amplifier circuit comprising the elements 239 to 293 is made identical with the clipper and amplifier circuit 272 t 282 in order to provide symmetrical conditions.

The resistor capacitor combinations 286, 287 and 295, 297 constitutes integrator networks in which the resistors may suitably be of about 1 megohm and the capacitors of about 2 microfarads. The potential developed across each capacitor 287 and 297 and applied to the grid of the associated tube 284, 294 will be proportional to the ratio of the average width of the significant portions between the edges 244 and 245 of the pulses 240' derived from the scanners 11 and 12 to the duration of the entire cycle. The load resistor 298 of the tube 284 and the load resistor 2199 of the tube 294 are connected to the opposite ends of a potentiometer 30) whose slider is connected to the D.C. line. The cathodes of the tubes 284 and 294 are connected to ground through a common cathode resistor 302.

The potentiometer 300 is adjusted so that the D.C. potentials on the plates of the tubes 284 and 294 are equal when the pulses from the differential amplifiers 15 and 16 are derived from exactly balanced bevels. In order to initially set the circuit shown in FIG. 12, a test blade whose bevels are exactly in balance is placed in front of the scanners and the potentiometer 300 is adjusted until the outputs from the tubes 234 and 294 are exactly equal. When now a blade strip whose adjacent bevels are out of balance is scanned, the pulses sent to the integrating circuits 286, 287 and 295, 297 will be of different widths which will be reected in the potentials on the capacitors 287 and 297 and hence in the D.C. potentials appearing on `the output terminals of the D.C. amplifier tubes 284 and 294. The D.C. output terminals of the tubes 284 and 294 are applied to the opposite ends of the deflection coil of the meter relay 21 and will result in a deflection of such meter in accordance with the sense and degree of bevel imbalance. It will be recalled that for the purposes of description it was assumed that the D.C. outputs from the tubes 284 and 294 will deflect the meter relay 21 in a positive sense when bevel 1 is too small or narrow with respect to bevel 3 with which it is compared and in a negative sense when bevel 3 is too small with respect to bevel 1.

The signal pulses derived from the bevels 2 and 4 are detected, amplified, clipped and integrated by circuits preferably identical with those described above in connection with the pulses derived from the bevels 1 and 3. The integrated potentials are amplified by amplifiers 44 and 46 (FIG. 1) identical with amplifiers 19 and 20 and the output potentials therefrom are compared in a meter relay which, in the apparatus described herein, is the same meter relay 21 that compares signals derived from the bevels 1 and 3.

HALF-WDTH DETECTOR AND COMPARATOR As described above in connection with FIGS. 9 and l0, the blade strip 10 runs through a supporting structure 185 which supports the strip by the center slots, and the carbide key 194 which is pressed against the sharpened blade strip edge by the spring 206 moves up or down in accordance with variations in the half-width of the strip. The key 194 is connected to the core 203 of the linear variable differential transformer 202 and the position of the key with respect to the physical assembly as a whole is reflected in an electrical signal at the output of the transformer. When the core -is centered in the transformer no output signal will appear across the output terminals of the transformer, indicating that the blade half-width is on target W hen the core is above the center position, an alternating signal of one phase will indicate that the blade half-width is too large, and when the core is below the center position, an alternating signal of the opposite phase will indicate that the blade half-width is too small. Since the amplitude of the error signals increases as the core moves away from the center position, the output signal from the differential transformer will indicate by phase and by amplitude the position of the carbide key and hence the half-width of the blade strip with reference to a predetermined standard.

Referring now to FIG. 13, the differential transformer 202 comprises an input winding 310, a pair of differentially connected output windings 312 and 313, and the core 203 connected to the carbide key 194 which is shown riding on the top edge of the moving sharpened blade strip 10. The upper terminal of the winding 313 is connected to ground, and the lower terminal is connected to the lower terminal of the winding 312, the upper terminal of which is connected through an isolating resistor 314 to the input 315 of a two stage amplifier 316. Also, connected to the input 315 of the amplifier 316 through an isolating resistor 318 of the same resistance as the resistor 314 is the output from a second differential transformer 323, which serves as a reference for the differential transformer 202 and which may be identical therewith except that the movable core 322 thereof is arranged for manual adjustment by means of a finger knob 328 mounted on the end of a micrometer stem 326 passing through an internally threaded micrometer mount 325 and secured to the core 322. An indicating dial 324 is provided below the knob 323 and the core 322 may be adjusted upwardly or downwardly as desired by turning the knob. The input winding 310 of the transformer 202 and the input winding 330 of the compensating transformer 320 are energized from a common source 332 of 5,000 cycle alternating current.

The output signal from the amplifier 316 is applied to a second two stage amplifier 334 through a band-pass filter comprising a capacitor 336 connected to ground through a branched network comprising a resistor 337 connected in parallel with series connected resistor 338 and capacitor 339. The capacitors 336 and 339 and the resistors 337 and 338 of the band-pass filter are chosen so as to provide a response curve that lwill peak at approximately the frequency used to excite the differential transformers, in this case 5,000 cycles per second. To this end, the capacitors 336 and 339 may have the values of 820 and 40 micromicrofarads, respectively, and the resistors 337 and 338 the values of 100,000 ohms and 91,000 ohms, respective- 

3. A CONTROL SYSTEM FOR A GRINDING MACHINE HAVING GRINDING HEADS FOR FORMING THE BEVELS OF AN EDGE ON A MOVING METAL STRIP AND MEANS FOR EFFECTING HEAD CORRECTION MOVEMENTS WITH RESPECT TO THE STRIP, COMPRISING MEANS FOR SCANNING EACH BEVEL TO DEVELOP A SIGNAL AS A FUNCTION OF THE WIDTH THEREOF AND MEANS FOR COMPARING SAID SIGNALS TO DEVELOP AN ERROR SIGNAL OF A SENSE CORRESPONDING TO THE SENSE OF DEVIATION FROM A DESIRED BEVEL WIDTH RELATIONSHIP AND OF A MAGNITUDE PROPORTIONAL TO THE AMOUNT OF DEVIATION, MEANS FOR PERIODICALLY SENSING SAID ERROR SIGNAL, MEANS RESPONSIVE TO THE SAMPLED ERROR SIGNAL FOR DETERMINING THE HEAD CORRECTION MOVEMENTS NECESSARY TO CORRECT FOR SAID DEVIATION AND MEANS FOR ACTUATING THE GRINDING HEADS IN ACCORDANCE WITH SUCH DETERMINATION. 